Roller, in particular a castor

ABSTRACT

The invention relates to a roller, especially a deflection roller (R), with a fork (2) bearing the tyred running wheel (1) and a braking device (25), at least for the rotary movement of the wheel (1), which has a push-rod (10) which can be moved towards the wheel (1) via an actuating device (1), a braking component (26) pressing into the tire (29) and a power storage spring (F) between the actuating device (11) and the braking device (11), and, in order to provide an easily used, tire saving braking device, proposes that the characteristic/prestress on the power storage spring (F) be designed in relation to the pressure resistance of the tire (29) in such a way that, in the braking position of the actuating device (11), in relation to the braking component (26), a determined depth of penetration into the tire (29) stopping the rotation of the wheel (1) is maintained and not exceeded.

FIELD AND BACKGROUND OF THE INVENTION

The invention relates to a roller, in particular a castor, having a forkcarrying the tired wheel and a braking device at least for therotational movement of the wheel, which braking device has a push-roddisplaceable towards the wheel by means of an actuating device, abraking member pressing into the tire, and an energy storage springinterposed between actuating device and braking member.

This type of roller is known from DE-GM 93 07 665. The construction inquestion seeks to achieve an ABS-style braking system. The aim istherefore to exert a highest possible braking force on the wheel in sucha way that blocking just about occurs, while continuing to maintain thewheel slip. Any additional force is diverted into the roller parts. Acomponent of the device in question is a push-rod, displaceable byexternal force, which has an energy storage spring interposed between anactuating device and braking member or which is itself set up as apush-rod resilient in itself. The braking member, which is pivotallymounted as a double-armed lever in the base of the fork, is providedwith an additional spring for the lifting of the braking component. Thepush-rod is inserted freely from above into the corresponding receivingportion of the roller.

SUMMARY OF THE INVENTION

In view of the above, it is an object of the present invention toproviding a roller of this kind in a manner which is more advantageousin use, while achieving a braking device which is less severe on tires.

As a result of the invention, a roller of this kind with increasedutility value is achieved: for example, the rapid wear to be observed inthe event of unsuitable tolerance pairings and/or incorrect mounting ofthe wheel may be substantially minimised. In practical terms, it isprovided that the characteristic/prestress of the energy storage springin relation to the pressure resistance of the tire is arranged so thatwhen the actuating device is in the braking position, the braking membermaintains but does not exceed a depth of penetration into the tirespecified for stopping the rotation of the wheel. Under the normal forceconditions, the push-rod operates like a rigid push-rod; it is only inthe event of higher braking-related resistance that the desired overloadsafety arrangement takes effect. The strength of the relatively hardenergy storage spring, which by far exceeds the effect of a restoringspring, thereby neutralises a part of the length of the push-rod strokeas set-up, precisely to the extent to prevent damage. In the long term,this brings about a substantial saving of the tire and keeps theactuating forces to be applied within the normal range. Furthermore, itis advantageous from a construction viewpoint for the energy storagespring to be disposed between an externally-controlled plate of theactuating device and a spring-biased slide member, which engages in theenergy storage spring and is biased by a second spring in the directionof the plate, which slide member is positioned at the one end of thepush-rod. Plate and slide member thus form the support for the energystorage spring, the two-part arrangement being further utilised so thatplate and slide member engage against one another before the energystorage spring bottoms, i.e. the turns of the spring close up. Thisenables exact consideration of the free space required for therespective type and size of roller. For this, an arbor portion of theplate engages in addition into a passage of the slide device. Thisprovide a non-tilting abutment for both of the ends of the energystorage spring. This construction may also be further used to the effectthat slide member and arbor portion of the plate are coupled positivelyin one another. A precise determination of the stop-limited spring pathmay thereby be achieved by simple means in that the positive coupling isformed by the head of a screw, whose screw-bolt side external edgeengages against a shoulder in the passage of the slide member. Finally,it also proves to be advantageous for the braking member to be arrangedto be adjustable in height relative to the push-rod at the other end ofthe push-rod. In this way, the initial adjustment and any subsequentadjustment which may become necessary as a result of wear may beachieved by the simplest possible means.

BRIEF DESCRIPTION OF THE DRAWINGS

With the above and other objects and advantages in view, the presentinvention will become more clearly understood in connection with thedetailed description of preferred embodiments, when considered with theaccompanying drawings, of which:

FIG. 1 shows in vertical cross-section, a roller in the form of acastor, with roll and deflection released,

FIG. 2 shows the same cross section with deflection blocked,

FIG. 3 shows a similar cross-section with the wheel in braking positionand deflection blocked (this basic construction carries a control cam atthe top, which can be operated either by an actuating lever or by acentral control device, not shown),

FIG. 4 shows a representation corresponding to FIG. 1 of a secondembodiment, once again with roll and deflection released,

FIG. 5 shows the same section with deflection blocked, and

FIG. 6 shows it with the wheel in braking position and with simultaneousblocking of deflection, actuated by a central control device, not shown,(the corresponding total locking is indicated in the basic constructionin accordance with FIGS. 1 to 3 by means of chain-dotted lines).

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The depicted castor R may be associated with hospital beds, which, forexample, have a central control device, by means of which blocking ofthe rolling movability of the wheel 1 and/or the pivoting movability ofa fork 2 may be selectively effected. Otherwise, there suffices anindividual actuation in this connection of the castors R using a controllever 3, which may be connected to the control lever of a neighbouringcastor by means of a transverse rod.

The control lever 3 actuates a control cam 5, which has a matching hubopening, by means of a polygon section 4, as shown for the basicconstruction of FIGS. 1 to 3.

From the back of the fork base 6 of the fork 2, there extends avertically upwardly directed pivot 8, with interposition of a ballbearing 7. The pivot 8 is sheathed by a sleeve 9, which is insertableinto a hollow foot of a bed frame or the like and secured therein inconventional manner.

The upper end of the sleeve 9 forms a bearing, aligned transversely tothe vertical, for the rotatable control cam 5.

A push-rod 10, which is vertical but secured against rotation, is housedin the interior of the hollow-formed pivot 8. This is moved from thetop-side towards the wheel 1 by an actuating device designated in itsentirety by reference 11. This takes place against the force of a spring12, which acts as return spring. The upper end position is to be seen inFIG. 2 and is stop-limited. The spring 12 is shown as screw-adjustablecompression spring. The latter projects into a bore 13 at the top. Thelower end turn of the spring 12 is supported on the annularshoulder-form base 14 of the bore 13.

The upper end turn of this spring 12 acts against the annular collar 15of a slide member 16, and more particularly against the underside of theannular collar.

The slide member 16 connects coaxially with the push-rod 10, upwards atthe top of the push-rod. It is screwed onto the latter in stop-limitedmanner. An annular shoulder 17 of the push-rod 10 forms thecorresponding limit stop. The portion of the push-rod 10, which extendsupwards beyond the annular shoulder 17, has external threading to engagein corresponding internal threading of the slide member 16 which ishollow throughout. The passage therethrough bears the reference numeral18.

The upper termination of the push-rod 10 is formed by a coaxiallymounted plate 19, as a part of the push-rod acting as lateraltransfer-function part of the actuating device 11.

As depicted in basic form, FIG. 1, the plate 19 is cam-controlled by theaforementioned control cam 5.

According to the second embodiment, FIG. 4, by contrast, there engages amember of an external control arrangement, not shown, such as forexample a Bowden cable, a pressure finger of which acts in a controlledstep-lift manner against the upper side of the plate 19.

The cam control provides a tooth 20 on the upper side of the plate 19,which tracks set-backs of differing depth and a circular curve sectionof the rotatable control cam 5, so that the running movability of thewheel 1 and/or of the pivoting movability of the fork 2 may be broughtabout by the basic position shown in FIGS. 1 and 4. The basic positionand the other positions are defined by the support at the top.

Between the plate 19 of the actuating device 11 and the slide member 16,which is urged by the spring 12 towards the plate 19, there is a energystorage spring F. This shown as a screw-adjustable compression spring.The slide member 16 projects into the interior of the energy storagespring F and thus forms a mount or guide for the cylindrically woundenergy storage spring F.

Making further use of the aforementioned annular collar 15, the energystorage spring F is supported by means of its end turn at collar 15 onthe upper side of the annular collar 15.

The upper end turn engages underneath the edge of the plate 19. In orderto obtain a good centering of the upper turn, the underside of the edgeis turned out, so that the base of the plate also projects with acentering effect into the interior of the energy storage spring F, butonly to approximately the depth of one turn cross-section of thisspring.

The sleeve 9 which is pushed onto and secured to the pivot 8 (omitted inthe embodiments of FIG. 4) produces the peripheral end of a holdingarrangement or spring chamber 21 formed in this way.

The plate 19 is held in axially limited manner on the slide member 16,to be displaceable but not to be removable (from the slide member). Forthis purpose, a shaft or arbor portion 22, which extends downwardsproceeding centrally from the base of the plate 19, engages in thestepped-formed passage 18 of the slide member 16. Slide member 16 andarbor portion 22 are positively coupled to one another. The positivecoupling bringing about the slide limitation is provided by the head 23'of a screw 23. The screw-bolt side external edge of the head 23' abutsagainst a shoulder 24 in the passage 18 of the slide member 16. The saidshoulder is formed by an internal projection caused by differingdimensions of diameter of the passage 18. The plate-side section of thepassage 18 is of lesser diameter than the section having the threadedbore. The shoulder 24 is directed downwards.

The arbor portion 22 has a threaded bore for the screw 23, proceedingfrom the free end of portion 22.

Between the upper face of the slide member 16 and the underside of theplate base of the plate 19, there is left an axial spacing x in thevertical direction. This permits an axial compression, i.e. shorteningof the push-rod 10, 19, against the force of the energy storage springF. The energy storage spring F is set up with a prestress such thatbefore a so-called bottoming of the turns of the energy storage springF, plate 19 and slide member 16 first of all come into abutment againstone another, so that operation can therefore only take place in theresilient region of the spring and bottoming does not occur.

At the lower end of the push-rod 10, there is a braking devicedesignated in its totality as 25. It is arranged at least to stop therolling motion of the wheel 1. An additional function is the blocking ofthe pivoting movability of the fork relative to the pivot 8. For thispurpose, the ball bearing 7 is interposed, so that the rotary movementof the fork 2 can take place about the vertical longitudinal centralaxis y-y of the pivot 8. The horizontal geometric axis z-z of the wheel1 is markedly displaced to the side of the vertical longitudinal centralaxis y-y.

A braking member 26, positioned at the lower end of the push-rod 10,serves to stop the wheel 1. It is disposed in a height-adjustable mannerat a lower portion of the push-rod 10, which lower portion has acorresponding thread, so that its roughened braking surface 27 can bebrought precisely to the operationally-correct basic position for acircular tread 28 of an elastic tire 29 of the wheel 1. As the brakingdirection is to the side of the uppermost point of the tire 29, thebraking member 26 is in the shape of a truncated cone, so that as aresult of its rotationally symmetrical braking surface 27, the sameconditions prevail in every rotational-angular disposition of thebraking member 26.

A toothed ring 30, which is installed behind the braking member 26,serves to block the pivoting movability of the fork 2. The toothed ring30 positioned in non-rotatable manner on the vertically displaceablepush-rod 10. Its downwardly-pointing teeth 31 cooperate with toothspaces 32 of a resilient blocking member, which enables a resilienturging of the teeth 31 into the spaces. On entering these (32), thepivoting movement of the fork 2 is blocked at the same time as therotational movement of the wheel 1 is stopped.

On the other hand, it is however also possible to block only thepivoting movement of the fork 2, as there are blocking projections 34 atthe top of the toothed ring 30, which can be engaged in matchingrecesses 35 of the fork base 6. In this situation, the push-rod 10assumes its highest possible displacement position.

Unnecessarily high levels of stress can be placed on the tread 28, andindeed on the whole tire 29 as a result of wear, unsuitable tolerancepairings, or also incorrect placement of the wheel 1. In order tocounteract this effectively and by simple means, thecharacteristic/prestress of the energy storage spring F, which is formedto be markedly stronger than the spring 12, is set up in relation to thepressure resistance of the tire 29 such that in the braking position(FIGS. 3, 6) of the actuating device 11, the braking member 26 maintainsand does not exceed a penetration depth into the tire 29, chosen to stopthe rotation of the wheel 1.

In the "loose" condition (see FIGS. 1 and 4), there is for example a gapof approximately 1 mm between the braking member 26 and the tread 28 ofthe wheel 1. In the "completely fixed" position (see FIGS. 3 and 6), thebraking component 26 digs for example approximately 2 mm into the tire29. For a roller of the type shown, this would require an actuatingforce of approximately 420 N.

If the roller R, or indeed the wheel 1, is incorrectly set, the brakingmember 26 must be pressed approximately 3 mm into the tire 26. The forceto be applied thus rises to approximately 900 N. In order to reduce thisincrease in force, the elastic element in the form of the energy storagespring F is interposed. The energy storage spring is for exampleprestressed to 420 N. If the wheel is incorrectly set, the energystorage spring F is compressed, thus compensating for part of the strokepath of the push-rod 10. Consequently, the braking member 26 is notpressed further into the relatively hard tire 29. The actuating forcethus, as has been discovered, only increases by 50 N instead of 480 N.

As an alternative to the arrangement shown, the energy storage spring Fmay also be installed at another suitable location, for example in theregion of the braking member 26, or even in what is called the switchbox, in which the control cam 5 is located.

I claim:
 1. A roller, in particular a castor (R), comprising a forkcarrying a rotatable wheel with a tire and a braking device adapted forbraking rotation of the wheel, a push-rod mounted displaceably towardsthe wheel and including an actuating device enabling displacement of thepush-rod towards the wheel, said braking device comprises a brakingmember mounted on a bottom portion of the push-rod so as to press intothe tire upon displacement of said push-rod towards said wheel into abraking position, and an energy storage spring operatively mounted so asto act against said braking member enabling an axial shortening of saidpush-rod against force of said energy storage spring, and wherein theenergy storage spring is prestressed in relation to pressure resistanceof the tire such that in the braking position, the braking membermaintains, without exceeding, a penetration depth into the tirespecified for stopping the rotation of the wheel.
 2. A roller, inparticularly a castor, comprisinga fork carrying a rotatable wheelhaving a tire, and a braking device adapted for braking rotation of therotatable wheel, a push-rod mounted displaceably towards the wheel, andincluding an actuating device for enabling displacing said push-rodtowards said wheel, said braking device has a braking member mounted onsaid push-rod and adapted to press into the tire upon displacement ofsaid push-rod towards said wheel, and an energy storage springoperatively interposed with prestressing between said actuating deviceand said push-rod enabling an axial shortening of the push-rod againstforce of said energy storage spring, the prestressing of the energystorage spring in relation to pressure resistance of the tire being suchthat in a wheel braking position of the actuating device, the brakingmember maintains, without exceeding, a penetration depth into the tirespecified for stopping rotation of the wheel.
 3. A roller according toclaim 2, further comprisinga spring-biased slide member engages in saidenergy storage spring, and is connected to said push-rod so as to be anintegral part of the latter, a second spring, said actuating devicecomprises an externally controlled plate, said energy storage spring isdisposed between said controlled plate spring-biased slide member, andsaid slide member is biased by said second spring in a direction towardthe plate, and said slide member is located adjacent a top end of thepush-rod and is spaced from and under said plate.
 4. A roller accordingto claim 3, wherein said plate and said slide member are displaceblymounted so as to enable engagement with one another in the brakingposition, said energy storage spring has turns, and the turns of theenergy storage spring are spaced apart so as to keep said energy storagespring in a resilient operative condition when said plate and slidemember are in engagement with one another.
 5. A roller according toclaim 3, wherein said plate has an arbor portion extending into apassage in the slide member.
 6. A roller according to claim 5, whereinsaid slide member and said arbor portion of the plate are coupleable toone another.
 7. A roller according to claim 6, further comprising ascrew having a head, and a downwardly facing shoulder formed in thepassage of the slide member, and wherein a releaseable coupling of saidplate and said arbor portion is formed by an upwardly facing portion ofsaid head of said screw which engages against said shoulder of the slidemember.
 8. A roller according to claim 2, wherein the braking member ismounted at a lower end of the push-rod adjustable in height with respectto the latter.